WIP: Do Popper.js overlays instead
This MR simply replaces Soapbox FE react-overlays with Popper.js elements as an alternative to !318 (closed).
Edit: I just rewrote this with a usePopper-based component.
I'm still struggling with the positioning and the Dropdown Menu component and would appreciate @alexgleason or anyone who knows Popper.js better's help with fixing this issue:
Edited by Sean King